This invention relates to log skidders or the like for dragging heavy loads such as logs through rough terrain.
In many operations, such as timber harvesting operations, it is often necessary to move, by dragging, loads such as logs over rough terrain. In a timber harvesting operation, for example, the point at which trees are felled may be quite remote from a loading point or the like. Consequently, skidding vehicles, such as log skidders, have been utilized to drag such loads across rough terrain from one point to another.
Many conventional log skidders in use today have fixed arch assemblies, that is, the boom-like assembly on the vehicle frame to which one end of the log to be skidded is attached as, for example, by a grapple or a fairlead and choker assembly. Because the end of the logs to be secured to the vehicle must be elevated to facilitate skidding, the arch assemblies extend a fair distance above the underlying terrain and, because the logs are to be dragged, the arch assembly is typically located near the rear of the vehicle. As a consequence, abrupt forces caused by the logs dragging over uneven terrain are directed to the vehicle at a relatively high location which produces rearward pitching of the vehicle and poor ground pressure distribution of the ground engaging means of the vehicle which produces ground disturbance and reduces traction. Obviously, rearward pitching is undesirable as an impediment to good handling qualities of the vehicle. Poor traction is undesirable due to its deleterious effect on vehicle handling qualities as well as promoting the possibility that the vehicle may become mired in a particular location. A high degree of ground disturbance is likewise undesirable, particularly where a vehicle must traverse substantially the same path several times since, as the ground progressively becomes more and more disturbed with each passing vehicle, traversing the path becomes increasingly difficult.
In an attempt to at least partially overcome one or more of the above difficulties, the prior art has resorted to pivoted arch assemblies and at least one log skidder having a pivoted arch assembly is commercially available today. In that vehicle, the arch extends rearwardly of the vehicle when logs are to be loaded and is pivoted forwardly on the vehicle to hoist the logs into a skidding condition. A choker type load carrying device is utilized and, as a consequence, the point of attachment of the fairlead when the arch is in a skidding position is relativey high on the vehicle and intermediate the ends of the vehicle frame. The latter factor improves weight distribution on the vehicle which includes traction and tends to reduce ground disturbance. However, because of the high location of the point of attachment of the fairlead, forces conveyed to the vehicle are applied thereto well above its center of gravity so that rearward pitching movements and any ground disturbances caused by such movement remain as problems accompanying the use of such vehicles.